package com.hmdp.service.impl;

import cn.hutool.core.util.BooleanUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import com.hmdp.dto.Result;
import com.hmdp.entity.Shop;
import com.hmdp.mapper.ShopMapper;
import com.hmdp.service.IShopService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hmdp.utils.RedisData;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import javax.annotation.Resource;

import java.time.LocalDateTime;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import static com.hmdp.utils.RedisConstants.*;

/**
 * <p>
 * 服务实现类
 * </p>
 *
 * @author 虎哥
 * @since 2021-12-22
 */
@Service
public class ShopServiceImpl extends ServiceImpl<ShopMapper, Shop> implements IShopService {

    @Resource
    private StringRedisTemplate stringRedisTemplate;

    //创建一个线程池（用于逻辑过期）
    private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);


    //通过id 查询 商户
    //先查找 redis，若redis没有再去 数据库查询商户信息，并且将信息保存到redis中
    @Override
    public Result queryById(Long id) {

        //第一种、解决 “缓存穿透”
        //Shop shop = queryWithPassThrough(id);
        //第二种，解决“缓存击穿”，利用互斥锁解决
        //Shop shop = queryWithMutex(id);
        //第三种，逻辑过期解决缓存击穿
        Shop shop = queryWithLogicalExpire(id);
        if (shop == null) {
            return Result.fail("店铺不存在");
        }

        return Result.ok(shop);
    }

    //缓存穿透
    public Shop queryWithPassThrough(Long id) {
        //1、从redis查询商户缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        //2、存在，直接返回
        if (StrUtil.isNotBlank(shopJson)) {
            //将字符串转变为 shop对象
            Shop shop = JSONUtil.toBean(shopJson, Shop.class);
            return shop;
        }
        //判断命中是否是空值
        if (shopJson != null) {
            return null;
        }

        //3、不存在，根据id查询数据库
        Shop shop = getById(id);
        //4、不存在，返回错误
        if (shop == null) {
            //如果商品的数据不存在，则为了避免频繁的出现 ”缓存击穿“的 问题，将缓存 空数据
            //将空值写入redis
            stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, "", CACHE_NULL_TTL, TimeUnit.MINUTES);
            return null;
        }
        //5、存在，先将信息写入redis,再返回
        stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(shop), 30L, TimeUnit.MINUTES);
        //6、返回
        return shop;
    }

    //缓存击穿
    public Shop queryWithMutex(Long id) {
        //1、从redis查询商户缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        //2、存在，直接返回
        if (StrUtil.isNotBlank(shopJson)) {
            //将字符串转变为 shop对象
            Shop shop = JSONUtil.toBean(shopJson, Shop.class);
            return shop;
        }
        //判断命中是否是空值
        if (shopJson != null) {
            return null;
        }

        //4、实现缓存重建
        String lockKey = null;
        Shop shop = null;
        try {
            //4.1获取互斥锁
            lockKey = "lock:shop:" + id;
            boolean isLock = tryLock(lockKey);
            //4.2、判断是否获取成功
            if (!isLock) {
                //4.3、失败，则休眠并重试
                Thread.sleep(50);
                return queryWithMutex(id);
            }
            //获取锁成功后需要再次检验Redis缓存是否存在（多线程引起）

            //4.4、成功，根据id查询数据库
            shop = getById(id);
            //模拟重建的延时
            Thread.sleep(200);
            //5、不存在，返回错误
            if (shop == null) {
                //将空值写入redis
                stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, "", CACHE_NULL_TTL, TimeUnit.MINUTES);
                //返回错误信息
                return null;
            }
            //6、存在，写入redis
            stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(shop), CACHE_SHOP_TTL, TimeUnit.MINUTES);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } finally {
            //7、释放互斥锁
            unlock(lockKey);
        }
        //8、返回
        return shop;
    }


    //缓存击穿_利用逻辑过期
    public Shop queryWithLogicalExpire(Long id) {
        //1、从redis中查询商铺缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        //2、判断是否命中,解释：因为利用逻辑过期，也就意味着缓存不会被删除，只会被更新。而缓存为空只能是店铺id有误或者不存在。
        if (StrUtil.isBlank(shopJson)) {
            //未命中，返回null
            return null;
        }
        //命中
        //判断缓存是否过期
        //将Json反序列化为对象
        RedisData shop = JSONUtil.toBean(shopJson, RedisData.class);
        JSONObject data = (JSONObject) shop.getData();
        Shop shop1 = JSONUtil.toBean(data, Shop.class);
        LocalDateTime expireTime = shop.getExpireTime();
        if (expireTime.isAfter(LocalDateTime.now())) { //通过expireTime 判断缓存是否过期
            //未过期，则返回商铺信息
            return shop1;
        }
        //过期
        //缓存重建
        //获取互斥锁
        String lockKey = LOCK_SHOP_KEY + id;
        //判断是否获取成功
        if (tryLock(lockKey)) {
            // TODO 成功，开启独立线程，实现缓存重建
            CACHE_REBUILD_EXECUTOR.submit(() -> {
                try {
                    //重建缓存
                    this.saveShop2Redis(id, 20L);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                } finally {
                    //释放锁
                    unlock(lockKey);
                }

            });
        }

        //返回 商铺信息（即使获取失败，则返回过期的商铺信息）
        return shop1;

    }

    //解决 缓存击穿
    //1、“上锁”
    private boolean tryLock(String key) {
        Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);

        return BooleanUtil.isTrue(flag);
    }

    //2、释放锁
    private void unlock(String key) {
        stringRedisTemplate.delete(key);
    }

    public void saveShop2Redis(Long id, Long expireSecond) throws InterruptedException {
        //1、查询店铺数据
        Shop shop = getById(id);
        Thread.sleep(200);
        //2、封装逻辑过期时间
        RedisData redisData = new RedisData();
        redisData.setData(shop);
        redisData.setExpireTime(LocalDateTime.now().plusSeconds(expireSecond));
        //3、写入Redis
        stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(redisData));
    }

    @Override
    @Transactional //添加事务特性

    public Result update(Shop shop) {
        Long id = shop.getId();
        if (id == null) {
            return Result.fail("店铺id不能为空！！！");
        }

        //1、更新数据库
        updateById(shop);
        //2、删除缓存
        stringRedisTemplate.delete(CACHE_SHOP_KEY + id);


        return Result.ok();
    }
}
